Beam plate structure having suppressor grid characteristics



Nov. 9, 1965 w. F. CULLEN 3,217,203

BEAM PLATE STRUCTURE HAVING SUPPRESSOR GRID CHARACTERISTICS Filed April 5, 1962 INVENTOR: WlLLlAM F. CULLEN,

I BY W EY.

United States Patent 3,217,203 BEAM PLATE STRUCTURE HAVING SUPPRES- SOR GRID CHARACTERISTICS William F. Cullen, Owensboro, Ky., assignor to General Electric Company, a corporation of New York Filed Apr. 5, 1962, Ser. No. 185,262 8 Claims. (Cl. 313-299) This invention relates to electrodes for use in electron discharge devices and, in particular, to novel beam-forming electrodes for electron discharge devices of the beam type.

In a pentode, the suppressor grid, which is normally at cathode potential provides a potential minimum in the plate-screen space to thereby prevent an interchange of secondary electrons between screen grid and plate. The resultant plate voltage-plate current characteristic of the pentode has what may be described as a rounded knee. In addition, the suppressor grid serves to electrostatically shield the plate from the control grid to thereby eliminate capacitive coupling between the external circuits associated with the control grid and the plate respectively. Prior-art pentode suppressor grids comprise wire helixes which have a high manufacturing cost and are difficult to handle due to fragility. In addition, the space requirement for the support rods precludes their use in tubes wherein the screen grid and the anode are closely spaced.

A beam tube, which is a type of tetrode or screen-grid tube, obtains suppressor grid action by accentuating the space-charge effects of the electrons flowing in the screenplate space. The suppressor grid action is effected by providing a relatively large screen-plate distance, by incorporating beam-forming plates, and by alignment of the control grid and screen grid wires. The alignment of the grids causes a focusing action resulting in sheet-like electron beams of high current density. The beam-forming or beam plates, which commonly are electrically at cathode potential, limit the lateral spread of the electron beams. The resulting space-charge or potential minimum between screen grid and plate, at high plate potentials, prevents the exchange of secondary electrons between screen and plate and the operation approaches that of a pentode. At low plate voltages, the resulting high space charge renders the plate current a function of plate voltage. The rapid transition between the two aforementioned conditions gives rise to a sharp knee in the plate voltageplate current characteristic curves.

It is often desirable to use a beam power tube having the characteristics of a pentode, i.e., having a more rounded knee in the plate voltage-plate current characteristic, better shielding between control grid and plate for lower capacitive coupling therebetween, and improved suppression of secondary electron currents between screen grid and plate.

It is an object of the invention to provide an improved electron discharge device.

It is an object of the invention to provide a beam plate which renders the characteristics and operation of a beam tube more similar to that of a pentode.

It is another object of the invention to provide a beam plate for an electron discharge device which causes the plate voltage-plate current characteristic of the device to have a more rounded knee, improves the electrostatic shielding between control grid and plate, and improves the suppression of secondary electron currents between screen grid and plate.

It is another object of the invention to provide an improved beam plate for an electron discharge device which will produce the above desired effects without substantially decreasing the plate current or increasing the screen grid current.

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It is a further object of the invention to provide an electron discharge device incorporating a rigid electrode which performs electrically like a wire helix suppressor grid in a pentode.

In accordance with the illustrated embodiment of the invention, improved performance of a beam tube is obtained by forming a window in the beam plate electrode, through which the electrons pass from cathode to anode, and providing spaced fingers extending from the beam plate electrode into the window area. The spaced fingers are formed to extend only partly across the window area and the individual fingers do not contact each other or the opposite side of the beam plate electrode, in order not to repel electrons in the current passing between cathode and anode. Thus, in accordance with the invention, the ends of the fingers extending from one edge of the beam plate electrode into the window area are spaced from the corresponding ends of the fingers extending from the opposite edge of the beam plate electrode into the Window area.

The subject matter of the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, may best be understood by reference to the following description taken in connection with the accompanying drawing, in which:

FIG. 1 is a partially cut-away isometric view of an electron discharge device incorporating the beam plate structure of the invention;

FIG. 2 is a perspective view of the beam plate structure of the invention; and

FIG. 3 is a cross-sectional View of an electron discharge device of FIG. 1, taken along the line III-III thereof, looking in the direction of the arrows.

FIGS. 1 and 3 illustrate the relative positions of the electrodes in a beam tube utilizing the beam plate electrode of the invention. A pair of insulative mica supports, such as mica disks 10, serve to support the various electrodes of the electron discharge device and maintain them in spaced relation. Snubbers 11 contact the interior wall of the tube envelope and provide lateral support for the electron discharge device within the envelope. The electrodes are normally mounted by inserting tabs, ears,

or rods extending therefrom into apertures in the mica supports. Cathode 12 is surrounded by and coaxial with control grid 13 and screen grid 14. Beam plate electrode 15, comprising side elements 16 and 17 and interconnecting straps 18, is interposed between screen grid 14 and anode 19. The beam plate is electrically connected to the cathode. Windows are formed in the beam plate electrode 15, as shown more clearly in FIG. 2, to permit the electron beams 20' and 21 to pass from cathode 12 to anode 19.

With reference to FIG. 2, beam plate 15 comprises side elements 16 and 17 which are joined by straps 18 interconnecting the respective ends of theside elements. Windows 24 and 25 are thereby formed in the structure and are defined generally by the side elements 16 and 17 and the straps 18. In accordance with the invention, fingers 30 are formed to extend from the side elements 16 and 17 into the window area but only partially across the window. Fingers 30 do not contact each other or the side element opposite that from which they extend. The number and the size of the fingers 30 may be selected in accordance with the tube type and the characteristics desired.

Fingers 30 extending into the window area, through which the beam passes from cathode to anode, are at cathode potential and operate to provide a stable potential minimum in the space between the screen grid and the anode. This potential minimum greatly reduces the passage of secondary electrons between the anode and the screen grid and the stability of this potential minimum, in contradistinction to the prior art beam tubes, results in a plate voltage-plate current characteristic having a rounded knee much like the knee found in pentode types having wire-wound suppressor grids. The magnitude of the anode current is not appreciably alfected in that, in accordance with the invention, the fingers 30 do not contact each other and do not extend all the way across the windows 24 and 25 and, thus, only a minimal part of the anode is directly shielded from the cathode emitting sur face by the fingers 30. The screen grid current is accordingly not appreciably increased due to electrons repelled by the fingers 30 extending from the beam plate 15. In addition, the beam plate electrode 15 serves to better electrostatically shield the anode 19 from the control grid 13. A further advantage is derived from the fact that beam plate 15 may be stamped from sheet stock and provides an inexpensive, rigid unit which is easily handled and which performs electrically like the more expensive wound suppressor grid of a pentode.

The beam plate structure shown has a generally rectangular cross-section, but may be formed with a circular, elliptical, or other cross-sectional shape depending upon the tube requirements. The side elements and the interconnecting straps may be formed integrally or the latter may comprise distinct elements bonded to the side elements. Ears 35 project from the top and bottom interconnecting straps 18 of the beam plate 15 and engage corresponding apertures in the mica supports.

While the fingers 30, extending from the side elements, are shown as being arranged in pairs and horizontally alined, it will be understood that such alinement is not required and may actually be replaced by a configuration of fingers that are oifset or stepped, as desired.

The electron discharge device, incorporating the beam plate electrode of the invention, can be mounted ina tube envelope 40, with the snubbers 11, extending from mica support disks and contacting the interior wall of the envelope 40 to provide lateral support for the electron discharge device. Leads 41 connect the various electrodes to the pin connectors 42 and serve to render the unit immovable axially within the envelope. The pin connectors 42 function to connect suitable sources of energizing po tential, not shown, to the electrodes.

Cathode 12 is shown extending through an aperture in the top mica support. Support rods 44 of control grid 13 and support rods 45 of screen grid 14 similarly protrude. Ears 35 of beam plate 15 and ears 46 of anode 19 also engage corresponding apertures in the mica supports. Anode 19 is cut away to more clearly illustrate the beam plate 15 and its position within the electron discharge device.

Although the invention and its operation has been described with reference to a specific embodiment, it is intended that the invention is not limited to the particular details shown and described which may be varied without departing from the spirit and scope of the in- (c) at least one spaced finger extending from said member into said aperture area transversely to said axis and only partially across said aperture area. 2. In an electron discharge device comprising a cathode,

an anode, and a grid coaxially arranged relative to a longitudinal axis of said device, said grid being between said cathode and anode, a beam plate electrode comprismg: i

(a) a pair of electrically connected members supported within the electron discharge device and disposed on opposite sides of the cathode between the screen grid and the anode,

(b) at least one window formed between corresponding opposing edges of said pair of members on either side of said cathode through which electrons pass, and

(c) a plurality of spaced fingers extending transversely to said axis only partially across said window from opposite edges of said pair of members.

3. An electron discharge device having cathode, anode, control grid, and screen grid electrodes coaxially arranged relative to a common longitudinal axis of said device, a beam plate electrode comprising:

(a) a metallic member of substantially rectangular cross-section supported within the electron discharge device surrounding the cathode and disposed in spaced relation between the screen grid and the anode,

(b) a pair of windows formed in said member on opposite sides of said cathode through which the electrons can pass from the cathode to the anode of the electron discharge device, and

(c) a plurality of longitudinally spaced fingers extending transversely to said axis and only partially across said window from opposite edges of said member, adjacent fingers from opposed edges also being spaced from each other.

4. A beam plate electrode comprising:

(a) a pair of side elements parallel to each other and to a longitudinal axis of said electrode,

(b) a plurality of straps connecting corresponding top and bottom edges of said side elements,

' (c) a plurality of spaced fingers extending transversely to said axis and only partially across said electrode from the oppositely disposed edges of said pair of side elements,

(d) said pair of side elements, said interconnecting straps, and said fingers defining a pair of oppositely disposed windows.

5. A beam plate electrode comprising:

(a) a pair of generally rectangular side elements adapted to be supported within an electron discharge device generally parallel to a longitudinal axis of said device and to be positioned on opposite sides of a cathode and between the screen grid and the anode of said device,

(b) a plurality of straps interconnecting the cone.

sponding corners of said pair of generally rectangular side elements,

(c) a pair of windows defined by the oppositely disposed edges of said pair of side elements and said interconnecting straps,

(d) a plurality of fingers extending transversely to said axis and only partially across the are-as of said pair of windows from the respective edges of the first of said pair of side elements, and

(e) a plurality of fingers extending partially across the areas of said pair of windows from the respective edges of the second of said pair of side elements and spaced from the corresponding fingers extending from the respective edges of the first of said. pair of side elements.

6. The beam plate electrode of claim 5 in which said plurality of fingers extending from said first and said second of said pair of side elements are parallel with said interconnection straps.

7. The beam plate electrode of claim 5, wherein pairs 5 6 of the fingers from said first and said second pairs of side member into the areas of said pair of windows for elements are in alinement. a distance less than one-half the dimension of the 8. In an electron discharge device having a cathode, windows.

screen grid and anode coaxially arranged about a common longitudinal axis, a beam plate electrode comprising: 5 References Cited y the Examine! (a) a metallic member of substantially rectangular UNITED S A S PATENTS cross-section supported within the electron discharge 2 228 978 1/41 Schade device surrounding said cathode and disposed in 2807738 9/57 Lieb 313 299 spaced relation between said screen grid and said 10 2860273 11/58 figfi anode,

(b) a pair of windows formed in said member on op- FOREIGN PATENTS posite sides of said cathode through Which the electrons pass from the cathode to the anode of the elecdlscharge dame and 15 JOHN W. HUCKERT, Primary Examiner.

(c) a plurality of spaced fingers extending perpendicularly to said axis and from opposite edges of said JAMES KALLAM, DAVID GALVIN, Exllmmers- 159,655 8/36 Germany. 

1. IN AN ELECTRON DISCHARGE DEVICE HAVING ANODE AND CATHODE ELECTRODES DISPOSED ALONG A COMMON LONGITUDINAL AXIS OF SAID DEVICE, A BEAM PLATE ELETRODE COMPRISING: (A) A MEMBER SUPPORTED WITHIN THE ELECTRON DISCHARGE DEVICE BETWEEN THE ANODE AND CATHODE ELECTRODES, (B) AN APERTURE FORMED IN SAID MEMBER THROUGH WHICH THAT ELECTRON BEAM MAY PASS FROM THE CATHODE TO THE ANODE, AND (C) AT LEAST ONE SPACED FINGER EXTENDING FROM SAID MEMBER INTO SAID APERTURE AREA TRANSVERSELY TO SAID AXIS AND ONLY PARTIALLY ACROSS SAID APERTURE AREA. 